It is well kown to employ an enzyme electrode in order to perform and monitor a bioelectrochemical reacton in aqueous solution. For example, an enzyme electrode involving glucose oxidase may be used to effect the oxidaton of glucose, and consequently to monitor the concentration of glucose in aqueous solution (see e.g. Turner et al, 1985). In such electrodes the enzyme is, conventionally, immobilised on the electrode by means of covalent bonding, and electron transfer between the redox centre of the enzyme and the electrode surface may be effected by means of a mediator molecule such as ferrocene (Cass et al 1984)
The use of enzyme electrodes in aqueous solutions enables the concentration of chemical substances in samples to be determined without extensive preparation. The enzyme provides the specificity of a biochemical reaction and the electrode monitors the extent or progress of the reaction in a sensitive manner (Turner et al, 1987).
However, the methods used to date suffer from several disadvantages. For example, the method is limited to the determination of species which are relatively water soluble, the electrode material must be one which is stable and operable in an aqueous solvent, and the method is not appropriate for use at elevated temperatures because of poor thermal stability of many enzymes in aqueous environments.
The present inventors have found that it is possible to carry out bioelectrochemical reactions in organic or microaqueous solvents. Although enzyme reactions in organic and microaqueous solvents have been reported (Klibanov, 1986; Halling, 1987; Kazandijan et al, 1985) the possibility of employing enzyme electrodes in organic electrochemisty has not, previously, been explored.